Various types of cuff transducers intended for use as electrical or chemical interfaces with neural tissue have been described in the literature. These nerve cuffs typically have a tubular bio-compatible dielectric material wall. In nerve cuffs designed to provide an electrical interface to tissues inside the nerve cuff, the inside of the nerve cuff wall supports one or more metal electrodes. Leads from the electrodes extend through and are supported by the nerve cuff wall. The nerve cuff walls must be sufficiently rigid to support the leads and electrodes. The leads may be connected to suitable signal-conditioning devices or electrical stimulation devices.
Nerve cuff electrodes have been used in stimulation systems with the goal of providing partial voluntary control of muscles that have been paralyzed as a result of lesions caused by spinal cord injury, stroke, or other central neurological system disorders. In some cases, partial motor function may be restored by stimulating motor neurons or muscles below the level of the lesion. Nerve cuffs may also be used as sources for the measurement of the neurological signal of the peripheral nervous system and for feedback of closed-loop functional electrical stimulation (FES) systems.
As such, there is increasing interest in the use of nerve cuffs to preferentially monitor and/or stimulate activity in selected axons within a nerve bundle. Hoffer et al., U.S. Pat. No. 5,824,027, which is incorporated herein by reference in its entirety, describes a multi-channel nerve cuff having longitudinal ridges extending along the interior walls of the nerve cuff.
The ridges divide the volume between the nerve cuff wall and the tissues within the nerve cuff into separate chambers. Electrodes are located in the chambers. This cuff structure can provide improved nerve signal recording selectivity and enhanced stimulation selectivity as compared to conventional nerve cuffs which lack separate chambers.
Fabricating a multi-chamber, multi-channel nerve cuff having one or more independent electrodes in each of several chambers is challenging, especially where the cuff is small in size. It is frequently desirable to provide nerve cuffs having internal diameters of only 2-3 mm. The challenge is compounded by the fact that such cuffs should be fabricated from material which is sufficiently flexible to minimize damage to delicate neural tissue, such as may occur with compression, sharp bending and/or stretching of the tissue. Suitable materials, such as bio-compatible silicone compositions may stretch when they are manipulated. This flexibility in the nerve cuff wall may make it difficult to place electrodes in precisely determined locations and to keep the electrodes in position.
Tyler, et al., U.S. Pat. No. 5,634,462, which is incorporated herein by reference in its entirety, describes multi-channel nerve cuffs constructed of stiff material. The Tyler et al. nerve cuffs are designed to deform and even penetrate a nerve, with the objective off approximating electrodes to more centrally located axons in nerves. A problem with this type of device is the possibility that the nerve could be damaged by the nerve cuff.
There is a need for methods to more readily accurately fabricate multi-channel nerve cuffs. Nerve cuffs used for making recordings of electrical activity within nerve tissues should provide good electrical isolation of the tissues within the nerve cuffs. There is also a need for nerve cuffs which may provide better isolation from externally generated electrical noise than is provided by current cuff designs. There is further needed a nerve cuff that may be used effectively to selectively stimulate or record from targeted subpopulations of nerve fibers in a nerve and may be used on nerves which could be damaged by penetration.